This invention relates to a new alumina and the method of preparing it. It also concerns the method for the preparation of aluminum hydroxychloride therefrom. More particularly, the alumina with which the present invention is concerned is a highly reactive alumina having a very high specific surface.
French patent application No. 73.36846, published under No. 2,247,425, describes active aluminas having a specific surface of at least 200 to 250 m.sup.2 /g. These active aluminas are prepared by partial dehydration of alumina hydrates (hydrargillite) in a stream of hot gases. This same French application describes the preparation of aluminum hydroxychlorides of the general formula Al.sub.2 (OH).sub.x Cl.sub.6-x which consists in reacting the above alumina with solutions of hydrochloric acid and/or aluminum chloride.
French application for certificate of addition No. 74.22968, published under No. 2,277,039, describes active aluminas having a specific surface of between 250 and 600 m.sup.2 per gram. They are obtained by partial dehydration of alumina gels obtained by precipitation of aluminum salts or of sodium aluminate. This French application also describes the use of this active alumina for the preparation of aluminum hydroxychlorides.
The active character of the aluminas used makes it possible to obtain aluminum hydroxychlorides in which "x" in the above formula may in the first case (active alumina obtained from hydrargillite) reach a value of 4 and in the second case (active alumina obtained from amorphous gels), a value of 5.
The interest which exists in being able to obtain aluminum hydroxychlorides of the general formula Al.sub.2 (OH).sub.x Cl.sub.6-x in which x=5 is known. It is from Al.sub.2 (OH).sub.5 Cl that alumina balls are prepared by the so-called "oil drop" or "salt gel" technique which is well known to those skilled in the art.
However, the alumina described in the aforementioned French Application for Certificate of Addition, while it makes it possible to obtain an aluminum hydroxychloride of the formula Al.sub.2 (OH).sub.5 Cl, has a certain number of drawbacks, the main ones being due to the structure itself of this alumina.
As a matter of fact, the activated alumina obtained by partial dehydration of amorphous gels contains a certain amount of gamma-alumina. This gamma-alumina reacts poorly in production of Al.sub.2 (OH).sub.5 Cl. Thus, the reaction of the alumina obtained from amorphous gels with solutions of hydrochloric acid and/or aluminum chloride is not quantitative, and the yield observed is only about 80 to 90%. Another drawback, which is related to the structure of the alumina used, resides in the rather long time of reaction required for the preparation of aluminum hydroxychloride. This reaction time is directly related to the specific surface of the alumina. As a matter of fact, the higher the specific surface, the greater the surface of contact and the faster the reaction velocity.
On the other hand, it is known from U.S. Pat. No. 4,053,579 that the decomposition at about 223.degree. C. of a special double carbonate of aluminum and ammonium gives alumina of gamma-structure, the area of this gamma-alumina being between about 200 and 400 m.sup.2 /g.
The foregoing clearly shows the interest which resides in being able to have alumina which has a specific surface and a crystallographic structure which are adapted to improve its reactivity.
The present invention achieves this purpose while obviating the drawbacks of the prior art which have been pointed out above.
It is, therefore, an object of the present invention to provide a new highly reactive alumina, especially adapted to produce aluminum hydroxychloride.
It is also an object of the present invention to provide a process for the preparation of the new highly reactive alumina.
It is a further object of the present invention to provide a process for producing aluminum hydroxychlorides from the new highly reactive aluminas.